Variable-pitch propeller



I.. T. FREDERICK.

VARIABLE FITCH PROPELLER.

APPLICATION FILED Dac. 30. 191e.

Patented Jan. 11, 1921.

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ATTORNEY UNITED STATES PATENT OFFICE.

LOUIS T. FREDERICK, OF WILKINSBURG', PENNgIf-LVANIA, ASSIGNOR TOWESTING- HOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OFPENNSYL- VAN IA.

VARIABLEFPITCH PROIPELLER.

Specication of Letters Patent.

Patented J an. 11, 1921.

Application led December 30, 1918. Serial No. 268,956.

.the provision of a variable pitch propeller of that type.

Propellers now in use are of a non-variable pitch typeI and, as aresult, they cause airplane engines driving them to run at differentspeeds, depending upon the blade thrusts under varying circumstances.For example, with a certain propeller of nonvariable' pitch type and anengine driving itV with the throttle wide o en the engine attained aspeed of 1410 M. while the plane, upon which the engine and propellerwere mounted, was blocked to the ground. During climb the engine speedincreased to 1450 R. P. and, in horizontal flight, ran at 15Q0 R. P. M.

These undesirable changes in engine speed are caused by changes oftorque imposed chiefly by the changes of the propeller pitch which, inturn, are caused partly by the iexibility or resiliency of the materialof which the propeller is made and partly because of certain necessaryinherent requirements of design.

More particularly, the object of my invention resides in overcoming, toa great extent, at least, changes in propeller pitch, caused byflexibilityof the propeller material, by

stiffening certain portions of the propeller relative to the remainingportions.

A still further object of my invention consists in accomplishing thestiii'ening' or reinforcing of certain portions of the propeller withoutthe addition of further material or of metallic stidening elements orthe like,

trated in the drawin s, in the several views of which corresponingnumerals indicate like parts, and then particularly pointed out in theclaims.

Figure 1v is a front elevation of a propeller, constructed inaccordancey with my invention; Fig. 2 is a transverse, sectional viewtaken through one of the propeller blades at substantially the linelI-II of Fig. l and Fig. 3 is a diagrammatic sectional view explanatoryof the principle upon which my invention is founded.

In a copending application filed by D. A. Dickey, on Dec. 30, 1918,bearing Serial. Number 268,949 and assigned to the Westinghouse Electric& Manufacturing Coinpany, is disclosed a propeller of composite typecomprising a plurality of superimposed layers of fibrous sheet material,such as duck, vimpregnated with a suitable hardened binder, such as aphenolic condensation product.

As there set forth, a propeller may be formed by cutting the severallayers or laminations, to the proper shapes and sizes, from a sheet ofthe impregnated duck, superimposing the layers thus formed in properrelative positions, dependent upon their shapes and sizes, and curingthe propeller body thus assembled by subjecting it to heat and pressure,in a suitably shaped mold, to compact the material and transform thebinder to its hard and substantially insoluble and infusible condition.

In practising my invention, I may construct a propeller by following themethod disclosed in the above mentioned application, superimposing theseveral layers of the impregnated sheet material employed in the mannerthere setl forth, with the layers disposed in planes substantiallyarallel to the faces of the propeller hub. y invention, however residesin the provision of means for sti ening the leading edges of the'blades, relative to the remaining portions of the blades, whereby Iproduce a variablepitch propeller.

To accomplish this, I may employ two or more different kinds of fibroussheet material, impregnated with a suitable binder, such as a phenoliccondensation product, the materials employed being such as to possessdifferent degrees of resiliency and locate the stiffer material in theleading edge portions of the blades of the propeller. Y

For example, referring more particularly to Figs. l and 2 of thedrawings", I have disclosed a propeller 1, the main body portion ofwhich may consist of superimposed layers 2 of duck', orequivalent-material, im-

regnated with a hardened phenolic condensation product and the leadingIedge portions or which may comprise correspondingly superimposedlayerslof another fibrous sheet material 3, such as paper, of propercharacter, impregnated with the same hardened binder. This propellermay, if desired, be provided with an outer coverin 4, of either duck orpaper or lother suitabIe material, which may be preferably impregnatedwith the saine binder as the body of the propeller and molded with therest of the propeller. Such a covering is not in any way, essential,however, and, if einployed, is provided chiefly to give the finishedpropeller a uniform and neat appearance.

A propeller constructed in accordance with my invention, with leadingedge portions of paper and trailing edge and body portions of duct, allimpregnated with a hardened binder, is Variable in pitch and farsuperior to the propellers now in use because of the stiffening of theleading edges of the blades caused by the localization of the stifferpaper material therein.

For a clearer understanding of the principle upon which my invention isfounded, attention is directed to Fig. 3 of the drawing which showsdiagrammatically, a sec-- tion of a propeller blade, looking toward thehub, with the direction of motion of the section, the pitch angle,leading and trailing edges and the up-stream and thrust faces clearlydesignated.

The air pressure is, of course, distributed, although not evenly, overthe entire thrust face of each propeller blade when the propeller is inaction and the whole blade section is pushed up stream, the resultant ofall distributed pressure acting through the center of pressure C. P. ofthe section, as shown. Strangely, however, this center of pressure isnearer the leading ed e lof the blade than the center of gravity Gr.,because of the necessary shaping of the blade, and, consequently, theresultant pressure, acting through the lever. arm L, tends to twist thesection in a counter-clockwise direction.

The result of this is an increase o f pitch angle and consequentincrease of torque and drag and a slowing downvof the engine.Furthermore, the greater the propeller thrust, the more pronounced thiseffect will be, which is just the reverse of what is desired as,formaximum efficiency, the pitch angle should decrease as the thrustincreases.

y practising my invention, I have provided a propeller in which theleading edges of the blades may be made rigid enough to hold u and allowthe trailing edges to defleet re atively more than the leading edges,when the thrust comes on, so that the pitch angle will be decreased asdesired, instead of being increased as the thrust is increased.

Obviously, while I have disclosed one method of practising my inventionand have specified the employment of certain materials, properlylocalized, in the body of the propeller, it will be clear that variouschanges, both in the method of forming the propeller and in thematerials employed, are possible. No limitations are, therefore, to beimposed upon my invention, other than those specified in the claims.

I claim as my invention:

l. A variablepitch propeller comprising a propeller body having itsleading edges a propeller body formed of superimpose layers 0f fibroussheet material impregnated with a hardened condensation product, as abinder, the sheet material in the leading edge portions being of greaterstiffness than that in the remainder of the body.

5. A variable-pitch propeller comprising a propeller .body formed ofsuperimposed la ers of fibrous sheet material impregnated with a binder,localized portions of the sheets being of one material whiletheremaining portions are of another material.

6. A variable-pitch propeller comprising a propeller body formed of'superimposed layers of fibrous sheet material impregnated with ahardened phenolic condensation product as a binder, those layers ofsheet material forming theleading edge portions of the body being ofpaper and the remaining portions of the body being of woven material.

In testimony whereof I have hereunto sulliscribed my name this 21st dayof Dec., 19 8.

LOUIS T. FREDERICK.

